A slide or gate valve assembly generally includes a housing defining a flow path extending between an inlet and an outlet. The slide valve assembly can, for example, be connected between a process chamber and a vacuum pump to form a portion of a high purity gas delivery system, such as those used in semiconductor manufacturing or other thin film coating processes performed at very low pressures (high vacuums), e.g., a pressure on the order of one torr or less. In such a case, a flange of the inlet of the valve assembly is secured to the process chamber while a flange of the outlet of the valve assembly is secured to the vacuum pump.
The slide valve assembly includes a slide plate that laterally moves, with respect to an axis of the valve assembly, between open and closed positions. In a pendulum-type slide valve assembly, slide plate is connected to a rotatably shaft by a pivot arm. In a completely opened position the slide plate is moved out of the flow path of the housing so that fluid can freely enter and exit the flow path, while in a closed position the slide plate is moved into close contact with a valve seat or annular surface surrounding the outlet of the valve assembly, so that conductance through the flow path is limited.
In a pendulum valve assembly, the movement of the slide plate usually requires rotational (i.e., pivotal or lateral) movement between the completely opened position and an intermediate position, and then at least some longitudinal (i.e., translational, linear or axial) movement from the intermediate position to the position where the slide plate is in close contact with the valve seat of the outlet. In order to obtain this combination of rotational and translational movement, some prior pendulum valves have typically used multiple actuator elements. The pendulum valve assembly helps control the flow of gas between the process chamber and the vacuum pump by controlling the position of the slide plate between the first opened position out of the flow path, the second opened position inside the flow path, and the minimum controllable conductance position against the valve seat.
Some existing pendulum valves utilize a seal ring to provide a complete seal (isolation) when the seal ring is independently actuated against the slide plate. A complete seal is useful, for example, during cleaning of the process chamber, and normally occurs only between semiconductor processing operations. U.S. Pat. No. 5,577,707 to Brida, for example, which is assigned to VAT Holding AG, discloses a pendulum-type slide valve including a housing having a flow channel, a slide plate for controlling flow through the channel, and a seal ring surrounding the flow channel. The seal ring is movable towards and away from the slide plate, when the slide plate is pivoted to a closed position. The seal ring is biased, using a spring or compressed air, against the slide plate when the latter is in its closed position, to tightly close the slide plate against the valve seat and to form a seal between the slide plate and the seal ring. The seal ring typically provides an isolation function for the valve assembly and is not used to control conductance. Normally the seal ring is held stationary and the slide plate is moved to control conductance.
It should be noted that the distance between the process chamber and the vacuum pump is preferably made as small as possible for various reasons, e.g., in order to conserve processing equipment manufacturing space and to maximize conductance between the process chamber and the vacuum pump. Accordingly, pendulum valve assemblies and other types of slide or gate valves are provided with a smallest possible dimension between outer flanges of the inlet and the outlet (i.e., “flange-to-flange dimension”).
One drawback for some existing gate or pendulum valves is that the valve provides poor control of flow (conductance) during the initial opening of the valve. For example, as the gate starts to clear the opening of the valve housing, the conductance increases rapidly. Since there is commonly an overlap between the gate and the opening (i.e., the gate has a larger diameter than the opening), initial movement of the gate results in little if any change in conductance. Thus, the overall conductance includes very little change in conductance followed by a very rapid change in conductance (and vice versa as the gate is closed), which results in poor control of conductance in this operating range of the valve.
One existing pendulum valve utilizes a rotating cam mechanism to improve conductance control. U.S. Pat. No. 6,089,537 to Olmsted, which is assigned to the assignee of the present invention and incorporated herein by reference, discloses an improved pendulum valve assembly that uses a simple rotating cam mechanism that precisely controls the rotational and longitudinal movement of the slide plate between a completely opened position and a completely closed position. The valve beneficially provides fine conductance control near the closed position. U.S. Pat. Nos. 6,161,576, 6,328,051 and 6,409,149, which are all assigned to the assignee of the present invention and incorporated herein by reference, also disclose improved pendulum valve assemblies and systems.
What is further desired, however, is a pendulum valve assembly that provides improved conductance without requiring an increase in the flange-to-flange dimension of the valve assembly.